This invention relates to self-regulating weirs and fishways.
Water control structures are well known devices, variously known as sluices, penstocks, gates or weirs, which control the flow of water by means of fixed or moving barriers. There is a special type of weir, known as a tilting or pivoted weir, in which the water flow is regulated by an inclined plane adjusted to different heights according to the upstream water level that is required. The dammed water builds up to the required level, before flowing over the edge of the weir to a lower level.
Water flow can, however, be erratic over any given period and frequent adjustment of a tilting weir can become necessary to suit changing conditions, particularly in order to release maximum flow in the case of flash floods. Also, by nature of its function, the weir may be difficult of access and distant from service facilities.
Ideally, therefore, a tilting or pivoted weir should meet the following requirements:
a) automatic self-regulation of water flow,
b) simple adjustment to vary the controlled water level that is required,
c) automatic response to flood or drought conditions,
d) automatic response to release floating clogging material,
e) availability of manual override,
f) mechanical operation independent of any external power source,
g) simple components requiring minimum attention,
h) the control gear should not be subject to abrasion or clogging by waterborne or submerged detritus,
i) facility to flush out submerged detritus,
j) the upstream level control has priority over downstream level,
k) all operations must be safe to use by a lone operator, and
l) there should be a facility for migratory fish movement.
It is an object of a first aspect of the present invention to provide an improved form of tilting or pivoted weir. It is a more specific object of said first aspect of the present invention to provide an improved form of self-regulating tilting or pivoted weir which meets all or substantially all of the above requirements.
In my British Patent Specification No. 2 294 079B, to which reference should be made, there is described and claimed a counterbalanced, self-regulating tilting weir comprising a tiltable weir gate over which the water flows, the weir gate being hinged at its lower edge to the base of a rectangular support frame and counterbalanced by float means located upstream of the weir gate so that the level of the weir is raised in response to a fall in the water level upstream of the weir gate and is lowered in response to an increase in the water level upstream of the weir gate, the weir gate being connected to the float means by chains which pass over sprockets mounted on an operating shaft carried by the frame, and means being provided for manual operation of the weir, over-riding the action of the float means and locking the weir gate in a desired position regardless of the water level.
It is a further object of the first aspect of the present invention to provide improvements in the tilting weir described and claimed in Patent Specification No. 2 294 079.
A second aspect of the present invention is concerned with the provision of a self-regulating fishway, allowing migratory fish to pass by an obstruction despite variations in river level upstream and downstream of the obstruction. If fluctuations in flow are excessive then a self-regulating tilting or pivoted weir can be used in parallel with the fishway to moderate the variations in water level to suit the self-regulating fishway.
Channels specifically designed to allow migratory fish to pass an obstruction are referred to herein as fishways. The most common fish pass profiles to be installed in fishway channels are of the vertical slot, Denil, or pool and weir type. Although there are other fish passage profiles in use throughout the world, the present invention is concerned primarily with fishways incorporating the proven profiles and dimensional relationships of the fish pass profiles referred to above.
Fishways are normally a fixture with an incline determined by the location and the habits of the local fish species. However, as mentioned above, river flows can be erratic for many different reasons and produce constantly changing levels. If a fishway is a fixture, it can be inundated as a result of excessive flow or can become ineffective if the upstream water level falls below the entrance sill. A manually adjustable entrance sill level may require frequent adjustment, while the location and function of the fishway can make it remote from a service base, with difficult access.
General elements of fishway/fish pass efficiency which are recognised as important to their design include the following:
a) the need to optimise the speed and success of fish passage to minimise delay, stress, damage and fallback of the fish,
b) the need to minimise water use where there are competing water requirements,
c) the need to maximise the range of stream flow under which the fishway is operable by matching the fish pass operation to flows during the period of desired fish passage,
d) the need to minimise construction, operation and maintenance costs by using construction methods and materials appropriate to the remoteness, geometric, hydrologic and geologic characteristics of the site, and
e) allowance for the clearance of debris.
It is an object of the second aspect of the present invention to provide an improved form of fishway, particularly a self-regulating fishway which meets the above requirements.
According to a first aspect of the present invention there is provided a counterbalanced, self-regulating tilting weir comprising a tiltable weir gate over which the water flows, the weir gate being hinged at its lower edge to the base of a support frame and counterbalanced by float means located upstream of the weir gate so that the level of the weir is raised in response to a fall in the water level upstream of the weir gate and is lowered in response to an increase in the water level upstream of the weir gate, the weir gate being connected to the float means by chains or cables which pass over pulley wheels, and means being provided for effecting vertical movement of the pulley wheels relative to the support frame.
The means for effecting vertical movement of the pulley wheels may comprise vertical lift spindles operated, via a worm gear, by means of a removable hand crank.
Means are preferably provided for adjustment of the operating angles of the chains or cables, and the weight, number and position of the floating counterbalances.
Means may also be provided for operating the weir manually overriding the automatic action and fixing the weir either fully open or fully closed as required, regardless of the flow conditions.
According to a second aspect of the present invention there is provided a self-regulating fishway comprising a tiltable chute containing a fish pass profile, the chute being arranged for tilting movement under the action of one or more floats positioned at or adjacent to the upstream end of the chute so that the required relative water depth is maintained at the chute entrance, the upstream level being so regulated that the chute incline does not exceed maximum desirable limit for the specific fish pass profile which is utilised.
The float or floats at the upstream end of the chute preferably incorporate a submersed buoyant bulb profile extending upstream of the chute entrance. The bulb profile acts in substantially the same way as that located just below the waterline on the bow of a modern commercial ship, diverting the main force of water to either side so that the majority of floating debris is deflected from the chute entrance, whilst desirable flow is maintained.
The flow through the self-regulating fishway is thus maintained substantially constant, providing a virtually debris-free flow from upstream and fish-attracting velocity at the downstream entrance.
Provision is preferably made for cables to be attached to both sides of the upstream end of the chute, the other ends of the cables being attached to the headwall, or other convenient point, in order to maintain the desired alignment of the fishway with the normal flow.
Regulation of the upstream water level for the self-regulating fishway is preferably provided by means of the self-regulating weir in accordance with the first aspect of the invention and the invention thus provides an installation comprising a self-regulating weir and a self-regulating fishway, each having the features defined above.